Contact lenses are generally produced by one of three general techniques--lathing, molding or spin-casting. Each technique has its advantages and disadvantages. For instance, lathing involves forming the anterior and posterior portion of the lens by cutting both surfaces from a disc of lens material. This technique is the most costly of the three manufacturing techniques but affords certain design freedoms not otherwise readily available using molding or spin casting.
Molding and spin-casting form the lens with few further processing steps. In both techniques, the anterior and posterior surfaces are formed in one step. Molding accomplishes this result by providing two mold surfaces which define the anterior and posterior of the lens. The spin casting process forms the anterior surface by providing a mold surface and the posterior surface by the forces generated by spinning the liquid monomer. Both techniques allow lower cost production of contact lenses than lathing due to the lower labor contact required to produce finished lenses.
However in both the spin-casting technique and in the molding technique, the lens adheres to the mold surface. This phenomena is an inevitable consequence of the spin-casting and the molding process and obvious because of the chemical interaction between the mold surface and the monomer mixture as the monomer is polymerized. Normally, this lens/mold interaction is overcome by hydrating the lens material which has the effect of weakening the interaction between mold and lens and also gently pulls the lens from the mold. Thus, the lens is in its soft form when it is first removed from the mold.
Cast contact lenses are rigorously inspected after casting to insure their optical performance and to avoid cosmetic effects and edge defects. These inspections are difficult to accomplish with soft lenses and requires significant labor to accomplish. Xerogel lenses (nonhydrated or hard lenses) are more readily inspected. Therefore, the cost of producing hydrogel lenses could be reduced by releasing hard lenses from the mold, inspecting the hard lenses and then hydrating the lenses until they had become hydrogels.
Various attempts have been made to release soft contact lenses from molds in their dry state. For instance, U.S. Pat. No. 2,542,286 teaches adding "lubricant" to optical devices made from resins.
U.S. Pat. No. 3,171,869 describes a method for releasing plastic lenses which comprises polymerizing the resin to a gel like state at 25.degree. C. to 125.degree. C. and then heating the gel to 125.degree. C. to 235.degree. C. until the hardened resin is formed.
U.S. Pat. No. 3,944,637 teaches using a specific comonomer mixture to achieve release from the mold. These three patents describe methods for releasing lenses from glass molds. Modern contact lens manufacturing is done in plastic molds as is evident from the teachings of U.S. Pat. No. 4,155,962 which teaches a method for releasing a xerogel lens from a mold container by applying force against the sides of the mold.
U.S. Pat. No. 4,159,292 teaches a method for controlling the release of contact lenses from plastic molds by providing the mold material with an internal lubricant.
U.S. Pat. No. 4,534,916 teaches adding surfactants to the comonomer to produce lenses with improved surface quality lenses. The use of such surfactants decreases the number of surface defects on the lens. The examples show that the lenses were removed from the molds in spincasting.